The present invention relates to a circular saw blade the periphery of which has been slotted so that the expansion of the peripheral part occurring when it warms up does not substantially change the state of tension of the blade.
The requirement for a satisfactory sawing result is that the circular saw blade maintains its plane shape and position on the entire range of operation even when its teeth have lost some of their sharpness. When necessary, the rigidity of the blade can be increased by thickening it or by applying suitable guiding means which alter the support of the blade so that the deformations caused by peripheral load are insignificant.
However, the greatest difficulty in handling the blade is caused by its liability to vibrate. The resonance frequencies which approach the rotational frequency of the blade are particularly dangerous. By stretching the centre section of the blade, that is by subjecting it to tension, the tangential stress of the outer periphery can be increased and thus the vibration frequencies can be transferred to a higher, safer range.
The stretching of a circular saw blade requires skill. The stretching must be adjusted to the drive speed, the friction caused by the guiding means and the peripheral load. The suitable degree of stretching can be found only by experimenting. The periphery expands due to the warming up of the peripheral portion of the blade which reduces the effect of stretching. The warming up occurs unevenly and depends on the degree of bluntness of the cutting teeth and the quality of the timber. The splinters pressed between the blade and the sawing slot and the saw dust leaking through the slots between the cutting teeth, in particular, cause rapid changes in the temperature of the periphery. Consequently, the blade may beging to vibrate at too high an amplitude which causes it to diverge from the sawing direction. This uncertainty diminishes the applicability of stretched circular saw blades provided with guiding means to multi-blade circular saws, in which saw type the divergence of one single blade stops the sawing operation and the great number of blades increases the number of breaks.
The actual shape of a stretched circular saw blade is difficult to measure. Thus during sawing a blade subjected to load has a different state of balance than what was intended when the setting was carried out. The deviation can exceed 1 mm in big blades. The local warming up of the blade changes its state of balance repeatedly. This phenomenon is particularly detrimental to double-shaft constructions in which the blades on both shafts should be in line.